Okenite Ca5Si9O23 ² 9H2O c 2001 Mineral Data Publishing, version 1.2 ° Crystal Data: Triclinic. Point Group: 1: As bladed crystals or laths, typically ¯brous with [010] as ¯ber axis. In aggregates of curved crystals, and compact radial ¯brous balls, to 4 cm. Twinning: About [010], composition plane 102 , lamellar. f g Physical Properties: Cleavage: Perfect on 001 . Tenacity: Elastic. Hardness = .5{5 f g D(meas.) = 2.28{2.33 D(calc.) = 2.33

Optical Properties: Transparent to translucent. Color: White, slightly yellow; in thin section, colorless. Luster: Vitreous to pearly. Optical Class: Biaxial ({). ® = 1.530 ¯ = 1.536 ° = 1.541{1.553 2V(meas.) = Large.

Cell Data: Space Group: P 1: a = 9.69(1) b = 7.28(1) c = 22.02(4) ® = 92:7(2)± ¯ = 100:1(3)± ° = 110:9(1)± Z = [2]

X-ray Powder Pattern: Bombay, India. 21 (vvs), 8.8 (vs), 3.56 (vs), 2.93 (vs), 3.07 (s), 3.05 (s), 2.98 (ms)

Chemistry: (1) (2)

SiO2 53.88 55.00 Al2O3 0.08 Fe2O3 0.01 CaO 27.61 28.51 SrO 0.27

Na2O 0.12 K2O 0.06 H2O 18.02 16.49 Total 100.05 100.00

(1) Bombay, India. (2) Ca5Si9O23 ² 9H2O:

Occurrence: Commonly in amygdules in basalts.

Association: Zeolites, apophyllite, prehnite, calcite, quartz, \chalcedony."

Distribution: From Greenland, at Qutdligssat (Kudlisat), Ritenbenk district; on Quqertarsuaq [Disko] Island, at Skarvefjeld and Bl½sedal, Godhavn district; and elsewhere. On Bordoy and Streymoy, Faeroe Islands. At Scawt Hill, near Larne, Co. Antrim, Ireland. On the Isle of Mull and on Morven Peak, Grampian Highlands, Scotland. In India, in Maharashtra, from the Syhadree Mountains; the Bombay quarry, Bombay; around Poona; and in the Nasik and Kolhapur districts. At Rio Putagan, Chile. In the Noche Buena mine, Mazapil, Zacatecas, Mexico. In the USA, at Crestmore, Riverside Co., California; in the Fairfax quarry, Centreville, Fairfax Co., Virginia; and at Skookumchuck Dam, near Bucoda, Thurston Co., Washington. In the Je®rey mine, Asbestos, Quebec, Canada. Other localities are known.

Name: For the German naturalist Lorenz Ocken (1779{1851), of Munich, Germany, the mineral name later shortened.

References: (1) Dana, E.S. (1892) Dana's system of mineralogy, (6th edition), 565. (2) Gard, J.A. and H.F.W. Taylor (1956) Okenite and nekoite (a new mineral). Mineral. Mag., 31, 5{20. (3) Heller, L. and H.F.W. Taylor (1956) Crystallographic data for the calcium silicates. H.M.

Stationary O±ce, London, 22{24. (4) Merlino, S. (1983) Okenite, Ca10Si18O46 ² 18H2O: the ¯rst example of a chain and sheet silicate. Amer. Mineral., 68, 614{622.

All rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise without the prior written permission of Mineral Data Publishing.